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S6 Chemistry: Alkanes and Alkenes (Paper 2: intermediate)
S6 Chemistry: Alkanes and Alkenes (Paper 2: intermediate)
Ten intermediate items on the isomers of pentane and hexane, ethanol from ethene, empirical and molecular formulas from percentages, oxygen for propene, carbon dioxide from a mass, an alkene found from bromine used, air needed by butane, substitution of ethane with chlorine, and addition against substitution.
Direct answers Answers in order: 3, 5, 46 g, CH2 and C3H6, 4.5 mol which is 108 dm3, 17.6 g, molar mass 70 which is C5H10, about 31 dm3, substitution giving chloroethane, and addition rather than substitution.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S6 Chemistry: Alkanes and Alkenes |
| Level | S6 |
02 Questions (10 items)
- FoundationHow many structural isomers does pentane, C5H12, have?
- FoundationHow many structural isomers does hexane, C6H14, have?
- FoundationOne mole of ethene undergoes addition with steam. What mass of ethanol is obtained?
- IntermediateA hydrocarbon contains 85.7 percent carbon and 14.3 percent hydrogen with a relative molecular mass of 42. Find its empirical and molecular formulas.
- IntermediateHow many moles of oxygen does one mole of propene need for complete combustion, and what volume is that at room conditions?
- IntermediateWhat mass of carbon dioxide is formed when 5.6 g of ethene burns completely?
- ChallengeExactly 16.0 g of bromine is used when 7.0 g of an alkene reacts completely by addition. Find its molar mass and molecular formula.
- ChallengeWhat volume of air is needed to burn 1 dm3 of butane completely, taking air as 21 percent oxygen?
- ChallengeWhat type of reaction occurs between ethane and chlorine under ultraviolet light, and what are the main products?
- Error redoA student writes that the reaction of an alkene with bromine is a substitution in which bromine replaces a hydrogen atom. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 3 | They are pentane, 2-methylbutane and 2,2-dimethylpropane. |
| 2 | 5 | Shortening the main chain from six carbon atoms down to four gives five different skeletons. |
| 3 | 46 g | The equation C2H4 plus H2O gives C2H5OH and the molar mass of ethanol is 46. |
| 4 | Empirical formula CH2 and molecular formula C3H6 | The empirical formula mass is 14 and 42 divided by 14 gives 3, so the molecular formula is C3H6, which is propene. |
| 5 | 4.5 mol, which is 108 dm3 | The equation C3H6 plus 4.5O2 gives 3CO2 plus 3H2O, and 4.5 times 24 gives 108 dm3. |
| 6 | 17.6 g | 5.6 divided by 28 gives 0.20 mol of ethene, which forms 0.40 mol of carbon dioxide, and 0.40 times 44 gives 17.6 g. |
| 7 | Molar mass 70 and molecular formula C5H10 | 16.0 divided by 160 gives 0.10 mol of bromine so the alkene is also 0.10 mol, and 7.0 divided by 0.10 gives 70. |
| 8 | About 31 dm3 | 1 dm3 of butane needs 6.5 dm3 of oxygen and 6.5 divided by 0.21 gives about 31 dm3 of air. |
| 9 | A substitution reaction giving chloroethane and hydrogen chloride | An alkane reacts by substitution under ultraviolet light where a hydrogen atom is replaced by a chlorine atom, not by addition. |
| 10 | The reaction is an addition in which the double bond opens and one bromine atom bonds to each carbon | No hydrogen atom is released in an addition and the product is a dibromo compound such as 1,2-dibromoethane. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
Write and balance the equation first, then convert with the mole ratio to mass or volume.Tutor Registration →
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